Long Term Evolution (LTE) femtocells are also called Home enhanced Node B (HeNB) in 3GPP terminology. They are miniature base stations intended to cover a small area in the order of 75 feet by 75 feet. From appearance, they look like a WiFi Access Point (AP) and are intended to be used just like an access point. For residential deployment, the femtocell is connected to a wire line broadband network in a similar fashion as the WiFi AP. The major difference is that femtocells normally operate in the cellular licensed spectrum while WiFi APs use the unlicensed spectrum. The immediate implications are first, femtocell service is a managed service whose providers are usually cellular operators, while WiFi services are best effort. Second, from the user perspective, the same cellular device (e.g. smart phone) that customers are using in the outdoor environment is also used inside the femto area, which is normally an indoor environment. Finally, femtocell performance is expected to be better than that of the macrocell environment due to the proximity of the femto base station to the user equipment and the generally higher capacity of the residential broadband network as the backhaul.
Femtocells are associated with different technologies: 2G (GSM, CDMA), 3G (UMTS, HSPA, and EVDO), and 4G (LTE, WiMAX). Currently in the United States, 3 out of the 4 largest cellular carriers have commercial deployment of either 2G or 3G femtocells. There are also many trials of femtocell service since 2008. ABI Research estimated that there are 60 trials of femtocell services at the end of 2009 over the world. While commercial trials of LTE femtocell have not been announced, there are a number of laboratory demonstrations. Moreover, many analysts have commented that the impact of LTE femtocell is expected to be even larger than those of the earlier generations. This is because while the 2G/3G femto introduction can be considered to be an afterthought, LTE femtocell is expected to be an integrated part of the LTE rollout planning.
While there is much promise about the femtocell idea, operators are still hesitating about large scale deployment. One of the concerns is that femtocells are expected to be deployed in the tens of thousands and all have to be managed smoothly without large operations cost. In particular, because of the uncertainty of femto locations and their potential proximity to each other as well as to the macrocell, interference can severely compromise femto performance. Moreover, malfunctioning or mistuned femtocells can further degrade the performance of the LTE macro network. All these concerns lead operators to focus on a new concept called Self-Organizing Networks (SON) as a long term solution, especially for operations. SON represents aggregated ideas that include “self-optimization”, “self-configuration”, and “self-healing”. These self-X capabilities are becoming integrated parts of the new 4G LTE network. The state of the art in various self-X technologies is still at their infancy.
The present invention proposes a framework targeted towards solving the management of large scale femtocell networks. A key feature of the invention is that while the optimization procedure involves only local femtocells without explicit coordination with other femtocells, there is a centralized counterpart of the localized algorithm, which oversees the global performance and sets policy and associated parameters. The proposed hybrid architecture ensures scalability, and provides better global control and assurance towards managing thousands of femtocells. In addition, the proposed framework and algorithms are general and can be applied to various radio technologies, including UMTS, WiMAX, and LTE. However, because of the importance of LTE and the associated OFDM technology, the following description will focus on using LTE to illustrate the invention.